Recognition of a state machine in high-level integrated circuit description language code

ABSTRACT

A method and apparatus for recognizing a state machine in circuit design in a high-level IC description language. The present invention analyzes high-level IC description language code, such as VHDL and Verilog®, of an IC design and extracts description information corresponding to a state machine. The description information can be, for example, the high-level IC description language code corresponding to the state machine, a state diagram of the state machine, a state table for the state machine, or other representation of the state machine. In one embodiment, the present invention identifies a set of one or more processes as defined by VHDL “process” statements. By identifying one or more clocked processes, one or more transition processes, and one or more output processes, the present invention provides a state machine summary to describe the state machine identified in the high-level IC description language code.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/140,633, filed Aug. 26, 1998, now U.S. Pat. No. 6,675,359, and issuedJan. 6, 2004, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to use of high-level integrated circuitdescription languages. More particularly, the present invention relatesto analysis of high-level integrated circuit description language toidentify code sequences defining integrated circuit implementations ofstate machines.

BACKGROUND OF THE INVENTION

High-level integrated circuit (IC) description languages such as VHDLand Verilog® are commonly used to design circuits. One embodiment ofVHDL is described in greater detail in “IEEE Standard VHDL LanguageReference Manual,” ANSI Std. 1076–1993, published Jun. 6, 1994. Oneembodiment of Verilog® is described in greater detail in “IEEE StandardHardware Description Language Based on the Verilog® Hardware DescriptionLanguage,” IEEE Standard 1364–1995, published Oct. 14, 1996. Thesehigh-level IC description languages allow a circuit designer to designand simulate circuits by using high-level code to describe the structureand/or behavior of the circuit being designed.

The high-level IC description language code is used to produce a netlistthat describes an interconnection of circuit components to providedesired functionality. The netlist can then be used to develop thelayout and ultimately fabricate an IC having the functionality of thedesigned circuit. The netlist can also be used for verificationpurposes.

Over time, many complex circuits have been designed using high-level ICdescription languages. The complexity of the code describing thecircuits increases with the complexity of the circuit described, whichin turn increases the cost of modifications to customize the circuit fornew environments especially if the code is poorly documented and/or theoriginal circuit designer is not available.

One component of a circuit design that is often modified to adapt thecircuit design to a new environment is the state machine. A statemachine is often used for control purposes, which is dependent on theenvironment in which the circuit design must operate. Therefore, inorder to modify the circuit design to operate in a new environment, thestate machine is often modified accordingly.

What is needed is a tool for recognizing and extracting state machinesfrom high-level IC description language code.

SUMMARY OF THE INVENTION

A method and apparatus for identifying a integrated circuit (IC)implementation of a state machine in high-level IC description languagecode is described. One or more transition processes within thehigh-level IC description language code are identified. A state machinesummary is built based at least in part on the one or more transitionprocesses identified.

In one embodiment, one or more clocked processes and one or more outputprocesses are also identified. A state machine summary is built based atleast in part on the one or more transition processes, the one or moreclocked processes and the one or more output processes. In oneembodiment, the state machine summary is a textual description of thestate machine. Alternatively, the state machine summary is a graphicalrepresentation of the state machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements.

FIG. 1 is one embodiment of a computer system suitable for use topractice the present invention.

FIG. 2 is one embodiment of a block diagram of a recognition andextraction process for extracting a state machine from high-level ICdescription language code.

FIGS. 3 a–3 n are one embodiment of VHDL code describing a state machineimplementation.

FIG. 4 is one embodiment of a flow diagram for recognizing a statemachine according to the present invention.

FIG. 5 is one embodiment of a flow diagram for identifying a clockedprocess according to the present invention.

FIG. 6 is one embodiment of a flow diagram for identifying a resetclause according to the present invention.

FIG. 7 is one embodiment of a flow diagram for identifying a clockclause according to the present invention.

FIG. 8 is one embodiment of a flow diagram for identifying a processproviding a next state assignment according to the present invention.

FIG. 9 is one embodiment of a flow diagram for identifying an outputprocess according to the present invention.

FIG. 10 is one embodiment of a flow diagram for building a state machinesummary according to the present invention.

FIG. 11 is one embodiment of a flow diagram for storing processinformation according to the present invention.

FIG. 12 is one embodiment of an output generated describing the statemachine of FIGS. 3 a–3 n according to the present invention.

DETAILED DESCRIPTION

A method and apparatus for recognizing and extracting a state machinerepresentation from high-level integrated (IC) description language codeis described. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention can be practicedwithout these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order to avoidobscuring the present invention.

Briefly, the present invention analyzes high-level IC descriptionlanguage code, such as VHDL and Verilog®, of an IC design and extractsdescription information corresponding to a state machine. Thedescription information can be, for example, the high-level ICdescription language code corresponding to the state machine, a statediagram of the state machine, a state table for the state machine, orother representation of the state machine. In one embodiment, thepresent invention identifies a set of one or more processes as definedby VHDL “process” statements. By identifying one or more clockedprocesses, one or more transition processes, and/or one or more outputprocesses, the present invention provides a state machine summary todescribe the state machine identified in the high-level IC descriptionlanguage code.

FIG. 1 is one embodiment of a computer system suitable for use topractice the present invention. Computer system 100 includes bus 101 orother communication device for communicating information, and processor102 coupled with bus 101 for processing information. Computer system 100further includes random access memory (RAM) or other dynamic storagedevice 104 (referred to as main memory), coupled to bus 101 for storinginformation and instructions to be executed by processor 102. Mainmemory 104 also can be used for storing temporary variables or otherintermediate information during execution of instructions by processor102. Computer system 100 also includes read only memory (ROM) and/orother static storage device 106 coupled to bus 101 for storing staticinformation and instructions for processor 102. Data storage device 107is coupled to bus 101 for storing information and instructions.

Data storage device 107 such as a magnetic disk or optical disc and itscorresponding drive can be coupled to computer system 100. Computersystem 100 can also be coupled via bus 101 to display device 121, suchas a cathode ray tube (CRT) or liquid crystal display (LCD), fordisplaying information to a computer user. Alphanumeric input device122, including alphanumeric and other keys, is typically coupled to bus101 for communicating information and command selections to processor102. Another type of user input device is cursor control 123, such as amouse, a trackball, or cursor direction keys for communicating directioninformation and command selections to processor 102 and for controllingcursor movement on display 121.

The present invention is related to the use of computer system 100 torecognize and extract a state machine from high-level IC descriptionlanguage code. According to one embodiment, recognition and extractionof state machine code from high-level IC description language code isperformed by computer system 100 in response to processor 102 executingsequences of instructions contained in memory 104. Execution of thesequences of instructions contained in memory 104 causes processor 102to recognize and extract state machine code in high-level IC descriptionlanguage code, as will be described hereafter.

Instructions are provided to main memory 104 from a storage device, suchas magnetic disk, CD-ROM, DVD, via a remote connection (e.g., over anetwork), etc. In alternative embodiments, hard-wired circuitry can beused in place of or in combination with software instructions toimplement the present invention. Thus, the present invention is notlimited to any specific combination of hardware circuitry and softwarestructure.

FIG. 2 is one embodiment of a block diagram of a recognition andextraction process for extracting a state machine from high-level ICdescription language code. The components of FIG. 2 analyze high-levelIC description language code for segments or sequences of instructionsthat define a state machine implementation in the IC circuit design.

The present invention is described below using block diagrams. Theblocks of the block diagrams are not intended to specifically denoteeither hardware or software implementation for components or devices.For example, the recognition and extraction engine can be a softwareentity that performs the functions described below, or the recognitionand extraction engine can be a hardware device designed to perform thefunctions described below. Alternatively, the recognition and extractionengine can be some combination of hardware and software. The high-levelIC description language code defining the state machine is recognizedand information is extracted from the high-level IC description languagecode and produced as output data. The extracted information describing astate machine can be used, for example, to generate a graphicalrepresentation of the state machine as described in U.S. Pat. No.6,480,985, which issued Nov. 12, 2002 and was filed Aug. 26, 1998,entitled “METHOD AND APPARATUS FOR GRAPHICALLY PRESENTING AN INTEGRATEDCIRCUIT DESIGN,” which is assigned to the corporate assignee of thepresent invention and hereby incorporated by reference. Alternatively,the output file can include a textual description of the state machineas is described in greater detail below.

High-level IC description language code 200 is any file or set of dataincluding code written according to a high-level IC descriptionlanguage. The present invention is generally described in terms of VHDLcode; however, any high-level IC description language, such as Verilog®can be used.

Analog/mixed-signal versions of high-level IC description languages(e.g., HDL-A™, VHDL-AMS, Verilog®-AMS) can also be used for high-levelIC description language code 200. One embodiment of VHDL-AMS isdescribed in greater detail in 1076.1 Language Design Committee, severalpapers under the generic name “White Papers”, IEEE 1076.1 Internal work,1996, and “1076.1 Working Document: Definition of Analog Extensions toIEEE Standard VHDL”, IEEE 1076.1 Committee Internal work, July, 1997.

High-level IC description language code 200 provides input torecognition and extraction engine 210. In one embodiment, recognitionand extraction engine 210 is a computer system, such as computer system100 of FIG. 1, executing a sequence of instructions to perform theprocess of recognition and extraction of state machine code; however,special purpose computer systems or other diagnostic or simulation toolscan also be used.

Recognition and extraction engine 210 generates an output that is statemachine description 220. In one embodiment, state machine description220 is a graphical representation of a state diagram corresponding tothe extracted state machine. Alternatively, state machine description220 is a textual or tabular representation of the state machine andcorresponding states.

In one embodiment, recognition and extraction engine 210 identifies thefollowing attributes for each state machine recognized: state variables,states for each state variable, one or more transition processes foreach state variable, a clock signal for the state machine, a resetsignal for the state machine, a clocked process for each state variable,and one or more output processes for each state variable. Othercombinations of attributes including some or all of the above attributescan also be used to describe a state machine.

In general, identifying one of the attributes listed above aids in theidentification of the remaining attributes. In addition, identificationof attributes can cause re-evaluation of previously identifiedattributes. Typically, identification of a clocked process is one of theeasier attributes to identify, therefore recognition starts withidentification of one or more clocked processes; however, recognitioncan start with identification of other attributes such as transitionprocesses. Also, identification of a clocked process simplifiesidentification of clock signal(s), reset signal(s) and state variables.

In one embodiment, state variables are identified before a transitionprocess is identified because a transition process is easier to findafter the state variables on which it operates are identified thanbefore. Output processes can then be identified, if necessary.

Identification of attributes is not required to proceed in the mannerdescribed; however, doing so can increase run-time performance. Becauseclocked processes are often the easiest attribute to identify, doing sofirst simplifies the overall state machine recognition process byreducing the number of processing iterations that are performed torecognize a state machine.

In one embodiment, attributes are recognized in the following order: aclocked process for each state variable, a reset signal, a clock signal,state variables, one or more transition processes for each statevariable, one or more output processes for each state variable, and thestates for each state variable. The last two attributes are easilyinterchanged because the two attributes are not interrelated.Alternatively, a transition process and state variables are identifiedto describe the state machine.

FIGS. 3 a–3 n are one embodiment of VHDL code describing a state machineimplementation. The state machine of FIGS. 3 a–3 n is a concurrent statemachine that can be recognized and extracted with the present invention.The state machine of FIGS. 3 a–3 n provides one embodiment of auniversal asynchronous receiver/transmitter (UART).

FIG. 4 is one embodiment of a flow diagram for recognizing a statemachine according to the present invention. In one embodiment, therecognition and extraction engine parses the high-level IC descriptionlanguage code to identify all processes, 410. The recognition andextraction engine identifies each “process” statement in VHDL code. Inthe example of FIGS. 3 a–3 n the following six processes are identified:machine0_clocked (FIG. 3 c); machine0_nextstate (FIG. 3 d);machine0_output (FIG. 3 g); machine1_clocked (FIG. 3 i);machine1_nextstate (FIG. 3 j); and machine1_output (FIG. 3 l). Whenparsing Verilog® code, the recognition and extraction engine identifies“always” or “initial” statements.

After the processes are identified, a subset of clocked processes areidentified, 420. In one embodiment, to determine whether a process is aclocked process, the recognition and extraction engine parses theprocess (or always/initial structure in Verilog®) for a condition thatchanges the state of the process on a clock transition. In the exampleof FIGS. 3 a–3 n, the following two clocked processes are identified:machine0_clocked (FIG. 3 c); and machine1_clocked (FIG. 3 i).

Transition processes are identified, 430. Transition processes areprocesses in which state assignments are made. For example, in the statemachine of FIGS. 3 a–3 n, the following two transition processes areidentified: machine0_nextstate (FIG. 3 d); and machine1_nextstate (FIG.3 j).

Output processes are identified, 440. Output processes are processesthat assign a value to a non-state variable output signal. For example,in the state machine of FIGS. 3 a–3 n, the following two outputprocesses are identified: machine0_output (FIG. 3 g); andmachine1_otuput (FIG. 3 l).

A state machine summary is built, 450. One embodiment of a state machinesummary is described in greater detail below with respect to FIG. 12.The state machine summary can be used, for example, to generate agraphical representation (470) of the state machine including a statediagram or a state table.

In one embodiment, an indicator of whether a state machine wasrecognized is generated, 460. The indicator can be used, for example, todetermine whether the recognition and extraction process shouldcontinue.

FIG. 5 is one embodiment of a flow diagram for identifying a clockedprocess according to the present invention. Both VHDL and Verilog®embodiments find IF statements to identify a state machineimplementation. An IF-THEN-ELSE statement in VHDL consists of:

IF <condition> THEN <then-part> [optional ELSIF part] [optional ELSEpart] ENDIF;

where [optional ELSIF part] is zero or more:

ELSIF <condition> THEN <else-if-then part>;

and [optional ELSE part] is zero or one:

ELSE <else part>.

Verilog® syntax is slightly different. In Verilog® an IF-THEN-ELSEstatement consists of:

if <condition> [optional else part];

where [optional else part] is:

else <else-statement>.

In Verilog® an <else-statement> may itself be an if statement, whichresults in:

else if <condition> <then-statement> else <else-statement>.

Each process is checked for a sensitivity list, 510. If the process doesnot have a sensitivity list and the process is not the final process at565, the next process is evaluated, 570. If the process is the finalprocess at 565, evaluation is complete.

If the process has a sensitivity list, the first IF statement in theprocess body is identified, 515. In one embodiment, the presentinvention assumes that the first IF statement includes “reset” and/or“clock” conditions. Alternatively, the first IF statement is notrequired to include the reset and/or clock conditions.

If an IF statement is not found at 520 and the process is not the finalprocess at 565, the next process is evaluated, 570. If an IF statementis found at 520, an associated ELSE or ELSIF part is sought, 525. If anELSE or ELSIF part (“else if” in Verilog®) is found at 530, the RESETclause is identified from the IF condition and corresponding THEN part,540. Identification of the reset clause is discussed in greater detailbelow.

If a reset clause is identified from the IF and THEN parts, the clockclause is identified from the ELSE or ELSIF parts, 545. If the IFstatement does not include ELSE or ELSIF parts, the clock clause isidentified from the IF and THEN parts, 535.

If the clock clause is identified the current and next state variablesare identified, 550. In one embodiment, the current process can bemarked as a transition process (not shown in FIG. 5). For example, ifthe current process is a clocked process and a transition process thatassigns state variables, the process is marked as a transition processat 550. Determining whether a process is a transition process isdescribed in greater detail below. The clocked process is checked forproper form at 560, which is described in greater detail below. If thecurrent process is not the last process at 565, the next process isevaluated, 570. If the current process is the final process, evaluationis complete.

FIG. 6 is one embodiment of a flow diagram for recognizing a resetclause of a state machine from corresponding high-level IC descriptionlanguage code. In one embodiment, the reset clause must be of the form“IF <reset_condition> THEN <action>”. In one embodiment, a condition isconsidered a reset condition when the condition tests for equality orinequality and a signal is checked against a constant or enumerationliteral.

The recognition and extraction engine 610 checks the form of the resetcondition, 610. The reset condition can include both constants andenumeration literal types. In one embodiment, the reset condition can beenclosed in parentheses and can include calls to the negation operatoror negation function.

If the reset clause is in the proper form, the recognition andextraction engine checks for the reset signal in the condition, 620. Forexample, “rst=‘0’” or “rst/=‘0’” can be used to describe the resetcondition. Other uses of the reset signal in the condition can also besupported.

If 610 and 620 are satisfied, the recognition and extraction enginechecks for an assignment to a state variable in the THEN part of thereset clause, 630. If 610, 620 and 630 are satisfied, the reset clauseis recognized. Otherwise, recognition ceases when a condition is notsatisfied.

FIG. 7 is one embodiment of a flow diagram for identifying a clockclause of a state machine from corresponding high-level IC descriptionlanguage code. The form of the clock condition is checked, 710. In oneembodiment, the form must be <IF or ELSIF> <clock_condition> THEN<action>. The condition is checked for the CLOCK signal, 720. In oneembodiment, the clock condition can be a function call with oneparameter (e.g., rising_edge(clk)) or an event test and level test(e.g., clk'event NAD clk=‘1’.

The action in the THEN part of the clock clause is checked for anassignment to a state variable, 730 or for a “case” statement test ofthe state variable, 740. If the clock clause is within a combinedclocked and transition process, the THEN part of the clock clausetypically contains a case statement testing the current state variable.if the clock clause is within a clocked process that is not a transitionprocess, the THEN part of the clock clause typically contains anassignment to the current state variable. The present invention testsfor both eventualities in order to identify the current state variablein either case. If 710, 720 and 730 or 740 are performed successfully,the CLOCK clause has been recognized. Otherwise, recognition ceases whena check is not satisfied.

FIG. 8 is one embodiment of a flow diagram for identifying a processthat provides a next state assignment according to the presentinvention. The description with respect to FIG. 8 identifies atransition process that is a clocked process. A process that is both atransition process and a clocked process can also be marked as atransition process as described above with respect to FIG. 5.

The process is checked to determine whether the process is a clockedprocess, 810. If the process is not a clocked process at 810 and theprocess is not the final process at 860, the next process to beevaluated is found, 870. If the process is a clocked process at 810, theprocess is checked to determine whether the process is a transitionprocess, 820. If the process has been previously marked as a transitionprocess at 820 and the process is not the final process at 860, the nextprocess to evaluate is found, 870.

If the process is not a transition process at 820, a process thatassigns to the next state variable of the clocked process is found, 830.If a process that assigns to the next state variable is found at 840,the process is marked as a transition process 850.

If a process is that assigns to the next state variable is not found at840 and the process is not the final process at 860, the next process isfound, 870. If a process is marked as a transition process at 850 andthe process is not the final process at 860, the next process is found.Otherwise, processing is complete.

FIG. 9 is one embodiment of a flow diagram for identifying an outputprocess according to the present invention. The flow of FIG. 9determines whether an output signal is assigned a value. Processes thatdetermine output signals are marked as output processes.

The process is checked to determine whether the process is a clockedprocess at 910. If the process is not a clocked process at 910 and theprocess is not the final process at 950, the next process is identifiedat 960. If the process is the final process at 950, the evaluationdescribed with respect to FIG. 9 is complete.

If the process is a clocked process at 910, a process that assigns to anoutput signal that is not a state variable is found at 920. The processidentified at 920 is an output process. If an output process is notfound at 930 and the process is not the final process at 950, the nextprocess to be evaluated is identified at 960. If the process is thefinal process at 950, the evaluation described with respect to FIG. 9 iscomplete.

If an output process is found at 930, the process is marked as an outputprocess at 940. If an output process is not found at 930 and the processis not the final process at 950, the next process to be evaluated isidentified at 960. If the process is the final process at 950, theevaluation described with respect to FIG. 9 is complete.

FIG. 10 is one embodiment of a flow diagram for building a state machinesummary according to the present invention. In one embodiment, the statemachine summary is used to provide information describing the behavioralcharacteristics of the state machine.

The process is checked to determine whether the process has a currentstate variable at 1000. If the process does not have a current statevariable at 1000 and the process is not the final process to beevaluated at 1080, the next process to be evaluated is identified at1090. If the process is the final process at 1080, the evaluationdescribed with respect to FIG. 10 is complete.

If the process has a current state variable at 1000, clock informationis stored at 1010. In one embodiment, clock information includes a clocksignal name and a clock signal type. Reset information is stored at1020. In one embodiment, reset information includes a reset signal nameand a reset signal type.

Current and next state information is stored at 1030. In one embodiment,current and next state information includes a current state variablename, a next state variable name and a state variable type. In oneembodiment, the next state variable and the current state variableshould be of the same type. Process information is stored at 1040.Storage of process information is described in greater detail below withrespect to FIG. 11.

A list of states is built at 1050. The number of the states in the listof states is compared to the number of states corresponding to theminimum number of states (“N”) required for the high-level descriptionlanguage code to be considered a state machine. In one embodiment, N=1;however, such an embodiment may result in an unacceptable number offalse positives, which can be the result of coding style. A falsepositive occurs when code that does not implement a state machine isrecognized as a state machine. In an alternative embodiment, N=2, whichprovides more reliable recognition than when N=1.

FIG. 11 is one embodiment of a flow diagram for storing processinformation according to the present invention. The information storedas described with respect to FIG. 11 provides information for building astate machine model. Additional or different information can also bestored in order to provide a different or augmented state machine model.In one embodiment, the evaluation described with respect to FIG. 11 isperformed for each process.

If the process is the first process that assigns the next state variableto the current state variable at 1100, the process is stored as theclocked process for the state variable at 1110. The clocked process fora state variable is the process that evaluates conditions that affectthe state of the state machine on clock transitions.

If the process is the first transition process for a particular statevariable or the first transition process that is not a clocked processat 1120, the process is stored as the transition process for the statevariable at 1130. The transition process for a particular state variableis the transition process that assigns values to the state variable.

If the process is the first output process for a state variable or thefirst output process that is not a clocked or transition process at1140, the process is stored as the output process for the state variableat 1150. The output process for the state variable is the process thatassigns values to output signals associated with the state variable.

FIG. 12 is one embodiment of an output generated describing the statemachine of FIGS. 3 a–3 n according to the present invention. The outputof FIG. 12 describes clock name and type, reset name and type, statevariable information for two state variables because the state machineof FIGS. 3 a–3 n is a concurrent state machine. Other output informationcan also be provided.

In the foregoing specification, the present invention has been describedwith reference to specific embodiments thereof. It will, however, beevident that various modifications and changes can be made theretowithout departing from the broader spirit and scope of the invention.The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A system for extracting a representation of a state machine fromhigh-level integrated circuit (IC) description language code,comprising: a recognition and extraction engine, wherein the recognitionand extraction engine is configured to identify one or more statevariables from the high-level IC description language code and whereinthe recognition and extraction engine also identifies one or more statesfor each of the state variables, one or more transition processes foreach of the state variables, one or more clocked processes for each ofthe state variables, and one or more output processes for each of thestate variables; and an output file, wherein the output file comprises astate machine description based on the one or more state variablesidentified by the recognition and extraction engine.
 2. The system ofclaim 1, wherein the recognition and extraction engine also identifies aclock signal for the state machine and a reset signal for the statemachine.
 3. The system of claim 1, wherein the recognition andextraction engine is implemented in software.
 4. The system of claim 1,wherein the recognition and extraction engine is implemented as part ofa hardware device.
 5. The system of claim 1, wherein each of thetransition processes is a process in which a state assignment is made.6. The system of claim 1, wherein each of the clocked processes is aprocess that changes the state of the process on a clock transition. 7.The system of claim 1, wherein each of the output processes is a processthat assigns a value to a non-state variable output signal.